1. Field of the Invention
Aspects of the present invention relate to a battery management system. More particularly, aspects of the present invention relate to a battery management system used in a vehicle using electrical energy.
2. Description of the Related Art
Vehicles having an internal combustion engine run with gasoline or heavy oil have caused serious air pollution. Accordingly, various efforts to develop electric or hybrid vehicles have recently been made to reduce air pollution.
An electric vehicle uses an electric motor powered by electrical energy output by a battery. Since the electric vehicle mainly uses a battery formed by one battery pack including a plurality of rechargeable/dischargeable secondary cells, advantages thereof includes no emission gases and less noise.
A hybrid vehicle commonly refers to a gasoline-electric hybrid vehicle which uses gasoline to power an internal-combustion engine and a battery to power an electric motor. Recently, hybrid vehicles that use an internal-combustion engine and fuel cells, and hybrid vehicles that use a battery and fuel cells have been developed. The fuel cells directly obtain electrical energy by generating a chemical reaction while hydrogen and oxygen are continuously provided.
Since battery performance directly affects a vehicle that uses electrical energy of the battery, each battery cell of the battery should perform well. Also, a battery management system (BMS) should measure a voltage and a current of the overall battery to efficiently manage charging/discharging operations of each battery cell.
In general, the battery management system uses a data table containing a relationship data of an open circuit voltage (OCV) to a state of charge (SOC) to estimate the SOC. When using the data table, the OCV should be precisely measured so as to precisely calculate the SOC.
When a vehicle is driven at a fixed speed or is stopped, and a charging and discharging operation of the battery is not performed, the OCV may not be precisely measured due to polarization of internal resistance of the battery. A time to dissipate the polarization should be sufficient to precisely measure the OCV. However, it is difficult to be guaranteed of such a time when a hybrid vehicle is driven. Accordingly, an error in the OCV measured during an insufficiently short time may cause an error in the calculating of the SOC.
In addition, since an error in controlling the battery to be charged and discharged is generated when an error in calculating the SOC occurs, the battery may be overcharged or over-discharged, which seriously affects battery performance.